This invention claims priority to German Application No. 10126064.4, filed May 28, 2001.
The invention relates to a method and apparatus for deep rolling recesses and radii on crankshafts according to the features of the preamble of the main claim.
The deep rolling of crankshafts is accomplished by means of deep-rolling rollers which are pressed with a predefined force into the recesses and radii which respectively laterally delimit the bearings of a crankshaft. A method, a machine or tools for deep rolling the radii and recesses of crankshafts are disclosed, for example, in EP 0 683 012 A1 and also in EP 0 661 137 B1 and EP 0 299 111 B1. In the known methods using the known machines the crankshaft material is plasticized to a depth of approximately 1 mm with the aid of deep-rolling rollers which are rotatably supported in the deep-rolling tool. In this case, residual compressive stresses build up tangentially around the rolling radius of the deep-rolling rollers, which reduce the formation of cracks at the critical points of the transition of the bearing pin to the cheek of the crankshaft during operation of the crankshaft under bending stress and thus appreciably enhance the fatigue strength of a crankshaft. The quality of any deep rolling is of decisive importance for the service life of a crankshaft. With higher torques and higher engine performance, especially with the widespread use of diesel engines, the requirements for crankshafts are becoming increasingly demanding. In consequence, the industry has moved towards making the deep rolling of crankshafts increasingly critical and with increasingly higher precision. So far it is known that deep rolling force can be carried out with a predefined deep rolling force. However, adhering to the deep-rolling force alone is not able to compensate for the spreads in the strength of the crankshaft material or the inaccuracies introduced into the crankshaft during the pre-processing of the crankshaft, especially during cutting and, if appropriate, hardening. Errors in the pre-processing at recesses or radii on a crankshaft to be deep-rolled are not detected by the known methods where a pre-defined deep-rolling force is adhered to.
A method for strengthening workpiece surfaces has also been disclosed in DE 195 11 882 A1. The known method can be applied to crankshaft processing. In this case, the workpiece surface is measured during the strengthening process and controlled variables for setting/changing tool parameters are derived from the measured results. The depth of penetration of the deforming tool into the workpiece surface is especially determined. A deep-rolling roller applying a corresponding pressing force penetrates into the material and thus produces ridges on both sides of the penetrating deep-rolling roller depending on the flow behavior of the work piece material. The actual penetration depth of the deep-rolling roller is then obtained from the difference in the ridges. The surface contour can then be measured in various different ways, for example, mechanically, pneumatically, hydraulically, acoustically, electromagnetically, electrocapacitatively or electronically using suitably acting sensors.
A disadvantage of the known method is the indirect recording of the penetration depth via the ridges on both sides of the penetrating deep-rolling roller. Such ridges are sometimes not present at all or are so little defined that they can barely be measured. This is especially the case, for example, with the ridges at the transitions to both sides of recesses on crankshafts which lie in respectively different planes. Experience has shown that the accuracy with which the ridges can be measured is not sufficient to make reliable statements on the depth of penetration of the deep-rolling roller into the crankshaft. Instead of this, it is substantially more favorable to directly follow the path of the deep-rolling roller, whether in the radial direction or in the axial direction of movement relative to the crankshaft, or in both directions of movement at the same time.
In industrial practice, the situation may also arise where individual deep-rolling rollers of a machine have a shorter service life compared with the other deep-rolling rollers and prematurely fail. With the means known so far, it is difficult or completely impossible to detect such premature failure of the deep-rolling tool. The industry has thus managed so far by randomly checking the rolled radii or recesses of crankshafts using clip-on instruments which are applied manually.
From the difficulties and disadvantages described previously, the object for the invention is to further improve the deep rolling of radii and recesses of crankshafts in order to achieve in particular a uniform product result and to detect in good time and eliminate any errors which have crept into the process from the preceding processing of the workpiece. In this way, the improvement should be attainable without additional expenditure and in an economical fashion. In particular, already existing equipment such as crankshaft deep-rolling machines and crankshaft deep-rolling tools as well as inherently known measuring and regulating equipment should be used to implement and the deep rolling without any substantial changes.
The present invention proposes an apparatus and method with which the penetration depth is measured continuously in the radial direction of the deep-rolling rollers of a deep-rolling tool and the magnitude of the deep-rolling force is regulated as a function of the measured penetration depth such that in the course of the deep-rolling operation at the recesses or radii of a journal bearing after deep rolling there is maintained a plastic deformation which corresponds to a pre-defined rolling depth.
In a similar fashion, errors which have been introduced into the crankshaft during the pre-processing, whether as a result of cutting or as a result of hardening, are detected. For this purpose there is used a measuring tool which has a structure identical to a deep-rolling tool. Before the actual beginning of the deep-rolling operation measuring rollers are inserted into the recesses of the journal bearings under a low applied force. The axial spreading of the measuring rollers which takes place during the penetration is recorded and determined as the measured value for the quality of the pre-processing. Sensors which record the axial distance between individual measuring rollers and the adjacent oil collars of the crankshaft are used for this purpose.
The known method of deep rolling the recesses and radii of crankshafts with a pre-defined rolling depth is now improved by achieving a specific rolling depth depending on the particular state of the radii or recesses of the crankshaft to be deep-rolled and suitably varying the deep-rolling force to achieve this rolling depth.
The apparatus can implement such a method using a single deep-rolling roller of a deep-rolling tool but the resulting penetration depth of both deep-rolling rollers usually used on a deep-rolling tool can also be measured. In addition, the resulting axial displacement of the measuring rollers of a measuring tool can be recorded. Several devices are suitable for measuring the penetration depth of the deep-rolling rollers or the displacement of the measuring rollers of a measuring tool in the axial direction and the particular selection is in each case within the measures of the relevant technical specialist.
The penetration depths of the deep-rolling rollers of a deep-rolling tool or the displacements of the measuring rollers of a measuring tool measured using sensors are fed to a computer, saved in the computer, converted into operands and the deep-rolling force is regulated accordingly. The usual procedure involves first rolling the crankshaft at a low and constant applied force before the actual deep rolling and, after the deep-rolling at the deep-rolling force, evaluating the difference between the measured values, which is obtained from the penetration depths at the applied force and the deep-rolling force and then determining the penetration depth using a correspondingly evaluated operand. Such an operand is advantageously suitable for determining the errors which occur during the pre-processing of the crankshaft, whether as a result of cutting or as a result of hardening or damage to the deep-rolling rollers themselves.
The present invention provides a radial intermediate space between the guide roller for the deep-rolling rollers and the journal bearing of the crankshaft there is provided a sensor which measures the penetration depth of the deep-rolling roller in the recesses and radii of the crankshaft. The sensor is connected to a computer which saves the measured values of the penetration depth and converts them into operands, where the computer is again connected to a plurality of control elements of which at least one controls the revolution of the crankshaft and at least one other controls the loading of the pressure-medium cylinder which the pressure medium as a function of the revolution of the crankshaft and the evaluated computer operands to produce the deep-rolling force.
Sensors can be arranged in various measuring planes along the equipment arms. In addition to the possibility of determining the penetration depth of the deep-rolling rollers into the crankshaft in the radial direction, provided that the two measuring rollers of a measuring tool configured as a deep-rolling tool are inclined at an angle of approximately 35xc2x0 within the measuring rolling tool, it is also possible to determine the axial spreading of the measuring rollers accompanying the penetration of the measuring rollers with the aid of sensors.
Inductive sensors, triangulation sensors which function optically, digital path-measuring sensors, potentiometers or ultrasound sensors are suitable as sensors. The choice of the most suitable sensor in each case lies with the relevant technical specialist. In this case, it is envisaged that triangulation sensors which operate with laser beams can also be used. Both digital path-measuring sensors and capacitative potentiometers can be constructed as devices which measure by the eddy current method. Preferably, the particular sensors have at least tenfold resolution with a measuring range of approximately 1 mm, where the measured value of the rolling depth lies between 0.1 and 0.9 mm.